The present invention refers to a roller press comprising a press roll and one or two cooperating pressure rolls, with particular application to a paper machine press section.
A roller press of this type is taught in Federal Republic of Germany Patent No. 959,702, corresponding to U.S. Pat. No. 2,855,829. It is there combined with a press section in a machine for the manufacture of paper and cellulose webs. In general, a roller press of this type can be used in wet presses and calenders and paper-making machines, as well as in plastic calenders and rolling mills.
In a known roller press or plant for the production of paper and cellulose webs, there is a pressure roll which is intended to be pressed against a fixed suction roll and there is a device for automatically lifting the pressure roll off the suction roll. Such lift occurs when the pressure prevailing in the suction line of the suction roll exceeds a given working pressure during the operation of the roller press, i.e. the required vacuum is no longer present in the suction line. The pressure roll is connected with a pressure cylinder which is finally activated when drying of the web of paper is no longer assured.
Brief variations in pressure are not recognized or responded to in the known design. In particular, disturbances on the suction roll which are limited in space are not recognized since measurements of the amount of air in the suction lines are too inaccurate for recognizing such deviations. For instance, entrained foreign bodies or folded regions of a pulp drainage felt, which are traveling through the press nip between the suction roll and the pressure roll, go unrecognized. For dependable operation of such a roller press and for the protection of the expensive roll coverings and pulp drainage felts, it is important that even brief, minor disturbances be rapidly and dependably recognized.